Niobium is in high strenth but the application in welder word steel and other structure steel

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Excel in steel is great to meaning of development of nearly 10 years of metallurgical industry, can satisfy the requirement of sex of intensity, plasticity, tenacity, figuration and weldability at present, make low cost rolled steel produces per year a quantity to occupy the 10 % of world structure steel to control. Review the development course of steel of high strenth structure. 20 centuries are earlier, the onefold breed steel that structural engineers use, this kind of steel is called " mild steel " , means " machine low carbon, flexibly, easily " , mild steel undertakes aggrandizement without the alloying element beyond designed use de-carbon, the Mn in steel is used at deoxidization, still contain stable sulfide, think mild steel is chemical commonly composition limits: 0. 1 % ~ 0. 25 % C, 0. 4 % ~ 0. 7 % Mn, 0. 1 % ~ 0. 5 % Si, the others is S, P and other element. Of mild steel succumb intensity is 250MPa about. It is before 1940, it is to increase tensile strength to the main demand of structural steel. To obtain relatively high strenth, c content increases to 0. 3 % , mn content is achieved 1. 5 % are controlled, the applied range of this kind of steel is not wide, cannot get used to the requirement of steel of structure of contemporary high strenth. It has following drawback: (A) ply obtains the rolled steel of 30mm, succumb intensity is too low, can achieve 360MPa only; (The range that intensity succumbs to drop when B) ply increases is very big; (Content of the C with tall C) , Mn makes the weldability of steel can become poor; (D) ruptures tenacity is lower than low intensity steel. With other material, especially the competition of the ferroconcrete, promoted the development of structural steel. To assure market share, developed a lot of handy production and fine technology, this makes the weldability to steel and breach concussion tenacity taller and taller. To 1942 ~ happen in bridge and shipping during 1949, especially famous " freedom annulus " the metal ruptures the investigation that behavior has and research, established a metal to rupture mechanical foundation. Basically improve the performance of steel through the following craft: Limit C content; Raise clean to be spent completely, include to reduce content of S, P; Al to oxigenate, microalloy is changed, often change rolling and the control rolling later. Afore-mentioned craft refined the organization of steel, raised the intensity of steel and tenacity. After 1960, castigatory introduced a few new steel grade in the standard: The NFA35 of DIN17102 standard of France, BS4360 standard of England, France - 504 standards. These national levels are become Europe unites a standard later -- , the foundation of EN10113 of fine grain steel. Already those who study duty ordered steel to fight brittleness to rupture decide principle. These jobs will normally result of breach concussion test and KIc value are used at rupturing mechanism. Below following condition, need material has taller tenacity: The engineering construction below fatigue load; Enlist in army lowly temperature; Tall succumb intensity; Large section rolled steel. New European structure designed a standard to include the temperature when result of the least impact is 27J, choose the content such as corresponding steel grade according to this. The arctic marine industry development of the area promoted the development of structural steel greatly, this area need matchs engineering construction in astringent microtherm condition remove theatrical makeup and costume. Because marine structure carrying capacity is finite, and the development as deep-sea oil and oily gas field, to marine structure character, reduce weight to become urgent matter, excel in steel makes a central point. Harsh to these environment issues use rolled steel, formulate special standard, be like EN10225 or API2MT2. Next watches generalized the characteristic that steel of contemporary structure steel plants. Steel grade of steel of the structure in expressing Europe and ASTM standard (30mm is thick, 634kg/m of unit weight ≤ )     -- -- -- -- -- -- -- -- -- -- -- , , .

2 1.

4 0.

045 0.

045 - - - - 0.

35   S235J0 0.

17 1.

4 0.

04 0.

04 - - - - 0.

EN10025 S275JR 0 of   of 35   .

21 1.

5 0.

045 0.

045 - - - - 0.

  of 4   (1993) S275J0 0.

18 1.

5 0.

04 0.

04 - - - - 0.

4   S355JR 0.

24 1.

6 0.

045 0.

045 0.

55 - - - 0.

45   S355J0 0.

2 1.

6 0.

04 0.

04 0.

55 - - - 0.

S355M 0 of 45   .

16 1.

6 0.

035 0.

03 0.

5 0.

02 0.

05 0.

1 0.

39   S355ML 0.

16 1.

6 0.

03 0.

025 0.

5 0.

02 0.

05 0.

1 0.

EN10113 of   of 39   - 1 S420M 0.

18 1.

7 0.

035 0.

03 0.

5 0.

02 0.

05 0.

12 0.

  of 45   (1993) S420ML 0.

18 1.

7 0.

03 0.

025 0.

5 0.

02 0.

05 0.

12 0.

S460M 0 of 45   .

18 1.

7 0.

035 0.

03 0.

6 0.

02 0.

05 0.

12 0.

46   S460ML 0.

18 1.

7 0.

03 0.

025 0.

6 0.

02 0.

05 0.

12 0.

46   S355G4 0.

16 1.

6 0.

035 0.

03 0.

5 0.

02 0.

05 0.

S355G11 0 of 1   .

14 1.

65 0.

025 0.

015 0.

55 0.

015 0.

04 0.

EN10225 S355G12 0 of   of   of 06   .

14 1.

65 0.

02 0.

007 0.

55 0.

015 0.

04 0.

06   S420G3 0.

14 1.

65 0.

025 0.

015 0.

55 0.

015 0.

05 0.

  of 08   (2000) S420G4 0.

14 1.

65 0.

02 0.

007 0.

55 0.

015 0.

05 0.

08   S460G3 0.

14 1.

7 0.

025 0.

015 0.

55 0.

015 0.

05 0.

08   S460G4 0.

14 1.

7 0.

02 0.

007 0.

55 0.

015 0.

05 0.

A36 of   of 08   (1997) 0.

26 0.

8 0.

04 0.

05 0.

4 - - -   Gr50 0.

23 1.

35 0.

04 0.

05 0.

4 - 0.

05 0.

A572 of   of 15   (1997)   Gr65 0.

23 1.

65 0.

04 0.

05 0.

4 - 0.

05 0.

A992 of   of 15   (1998) Gr50 0.

23 1.

5 0.

035 0.

045 0.

4 - 0.

05 0.

Gr50 0 of 11   .

12 1.

6 0.

03 0.

03 0.

4 - 0.

05 0.

06 0.

A913 of   of 38   (1997) Gr65 0.

16 1.

6 0.

03 0.

03 0.

4 - 0.

05 0.

06 0.

43     -- -- -- -- -- -- -- -- -- -- -- -- --A5d ASTM standard: A200     1. Material of manufacturing technology strip can use aerobic converter smelt already, also can use smelt of electric arc furnace, use the craft that connect casting morely to produce. Lian Zhu becomes small square base, big billet and flat ingot, as semi-manufactured goods, also become even casting I-steel figure recently. According to the experiment 1964, what began I-steel 1968 is close eventually form cast. This technology is mixed by iron and steel of plain Qi of Japan, Japan later the Ato of  of button division Yam of Japanese steel tube, United States, Chaparrol and company of northwest iron and steel, company such as European ProfilARBED is used. The semi-manufactured goods of the different type of product of hot-rolling of company of European PrefilARBED group. The biggest width of labour word bridge amounts to 1118mm, the biggest perhaps ply achieves 125mm. The proportion that hot-rolling I-steel takes structural steel is very large. Accordingly although the discussion below is centered at I-steel, but its are main the other rolled steel that the principle applies to equivalent ply likewise. The molten steel that ProfilARBED company produces big I-steel by smelt of electric arc furnace, lian Zhu becomes I-steel. After Lian Zhu, first before make friends, i-steel is entered in the pace heat afresh in furnace, by rolling of two reversible and all-purpose rolling mill and by all-purpose rolling mill eventually make friends. Rolling mill pass is different, the section of rolling product is different. 1. The semi-finished products of traditional rolling technology of 1 big I-steel is heated to be controlled to 1250 ℃ , via 15 ~ 20 second rolling. And to ingot casting, need to heat 1300 ℃ , the likelihood needs via 40 second rolling, the path of I-steel second press next rate to be 4 % ~ 20 % , eventually prep above of make friends temperature 1000 ℃ , the temperature on labour word bridge distributings inhomogenous: Root ministry and lumbar joint temperature are highest, intermediate temperature lowest of the waist, the dimension of the difference of temperature and I-steel is concerned, the biggest difference in temperature can amount to 100 ℃ . Press this craft rolling, have grade by ASTM standard, ply is 7 class for the I-steel brilliant granuality of 40mm. To refine the organization of steel, can use Ti - Nb microalloy is changed, grain of the austenite when making heat again is quite petty (amount to 50 μ M, is not 200 ~ 300 μ M) , recrystallization organization is quite petty also. Lab imitate result shows, every organization that presses next rate to amount to 15 % to be able to obtain a need, mechanical function achieves 50Ksi (50Ksi of tensile strength ≥ , be equivalent to S355) . Express the 2 chemical composition that are 50Ksi I-steel. This composition design is used successfully already at industry to produce. The temperature in hot-rolling process is high, the Nb in meaning steel still holds solid dissolve position, although be in eventually when make friends temperature, also do not have the carbide separate out of Nb. When Nb exists with solid dissolve condition in steel, change through defer photograph, refine ferrite grain, acquire system of a certain quantity of shellfish family name, increase the strength of steel thereby. The typical organization of this steel is the ferrite of about 80 % , the others is body of shellfish family name and pearlite. Below condition of identical rolling craft, press ASTM standard judgement, c - the brilliant granuality of Mn steel is 7 class, and the brilliant granuality of the steel that contain Nb is 9 class. Change process medium or after changing, if NbC precipitate is formed in ferrite, criterion the intensity of steel can rise further. Refine grain can finitely only through traditional rolling craft, be more than the steel of 20mm to 50Ksi of intensity prep above or ply, to satisfy tenacity requirement, must use control rolling technology. 1. Normalizing of 2 normalizing heat treatment is change in Ac3 photograph bit of above (normally Ac3 + 50 ℃ ) . The organization of condition of S355 steel hot-rolling is ferrite - pearlite, the objective that undertakes normalizing is handled is to refine an organization, make an organization even, raise the tenacity of steel. The degree that the organization refines and primitive organization are concerned. To cannot undertaking controlling the steel of rolling, especially thick sectional rolled steel, can achieve through normalizing refine grain effect very well. To small sectional steel products, normalizing is likely the purpose that short of refines, below this kind of circumstance, this rolling process can consider as control rolling craft, say normally for " often change rolling " , the organization after the organization of hot-rolling condition and function and normalizing and performance are similar. Increase the tensile strength of normalizing steel with Nb normally, nb can prevent austenite grain to be brought up, enlarge γ photograph area. In the steel that contain Si, this kind of effect particularly apparent. Normalizing temperature is mixed in 900 ℃ between 1050 ℃ , nb content is 0. 02 % ~ 0. 04 % , make with respect to enough brilliant granuality reachs 10 level. As contrary as this, when Nb is not being contained in the steel that contain Si, when normalizing temperature is 1000 ℃ , brilliant granuality is 7 class. The carbolic nitrification of Nb the nitride of content and Al is same, still can prevent austenite grain to be brought up in 1050 ℃ , this kind of action is attached most importance to especially should, although be in the heat treatment furnace with inhomogenous furnace temperature, also can obtain petty ferrite - pearlite organization. Ply is different, the brilliant granuality of hot-rolling condition I-steel is 7 ~ 9 class. The brilliant granuality of 30 ′ of × of the 910 ℃ after normalizing reached 11 level. 40 ℃ of VT27 > . < of the VT27 after normalizing - 45 ℃ , after normalizing, intensity all drops somewhat. According to above test result, formulate the alloy of S355 steel designs a principle. Solder to satisfy the requirement of function, must have inferior carbolic equivalent. With accuse steel rolling photograph to compare, s460 steel has taller carbolic equivalent, restricted its output thereby. Still must point out, be opposite especially small sectional steel products, heat treatment is easy bring about be out of shape. Straightening machine Jiao Zhi must be used after be out of shape. 1. 3 craft charging press hard against each other: When controlling rolling to undertake controlling rolling in the microtherm area of austenite, the steel that contain Nb can satisfy the requirement of intensity tenacity. In rolling process, austenite undertakes is out of shape in 1050 ℃ above above all, make austenite grain is refined. If give,always press next rate to be 70 % , criterion after every second rolling, pass static recrystallization attainable petty austenite grain. Wait for next lukewarm undertake below to 900 ℃ eventually make friends. The recrystallization in the steel that contain Nb is very slow, austenite grain turns cake into shape, refined grain effectively thereby. The steel containing Si of smelt of electric arc furnace, high free nitrogen content is right of function rise very remarkable. In afore-mentioned steel, complete nitrogen content is in 100ppm above. In the empty Leng Gang that contains Si, free nitrogen content and relation of complete nitrogen content are N free = 0. 43N is complete. The tenacity of the steel that contain Si and free nitrogen content are concerned. Free nitrogen content is when 32 ~ 33ppm is the following, VT40J is about - 10 ℃ . Once free nitrogen content exceeds 35ppm, VT40J achieves > + quickly 30 ℃ . Raise tenacity method to have two: It is will eventually make friends temperature reduces 870 ℃ from 960 ℃ , make ferrite brilliant granuality raises 9 level from 7 class, this craft raised the tenacity of steel significantly; 2 it is to use control rolling, form nitride, reduce nitrogen of the freedom in steel. Collaboration of both put together is used, the tenacity of steel is best. Commonly used Al will reduce content of nitrogen of the freedom in steel, also can introduce the element such as Ti, Nb, V. Photograph comparing is mixed at Al Ti, v and Nb have an advantage, they won't bring about Lian Zhu to water mouth appears to jam in the process or produce the problem connecting casting such as blemish. To free nitrogen content determine the effect that can be used at deciding nitride forms an element to secure nitrogen. Decided Al is equivalent from this V of + of Nb of + of 2Ti of + of Al of = of computational formula Aleq (% ) . According to the mechanical function of I-steel the demand chooses alloying element, VT40 and succumb the function of intensity concerns. Use V of + of Al, Ti, Al + Ti, Ti to undertake microalloy is changed, succumb when intensity is 320MPa about, VT40 is in - 60 ~ - between 70 ℃ , intensity and use at relative C - Mn steel is similar, c - there is precipitation sclerosis in Mn steel. Of Nb microalloy steel succumb when intensity is 375MPa, VT40 = - 55 ℃ , nb produced distinct precipitation sclerosis effect, refined an organization. Ti + Nb is compound when joining, as a result of the interaction of TiN and Nb, make precipitation sclerosis effect is reduced somewhat. No less, contain the sclerotic effect that Ti adds to also reduce V in V steel, because Ti secured nitrogen, reduced the sclerotic effect of the nitride of V. Although control rolling to be able to achieve the requirement of intensity and tenacity, but also put in a few defect. Reduce eventually the load that make friends temperature increased rolling mill, a lot of rolling mill are when the design and did not consider the load that this share increases. With C - Mn steel photograph is compared, because the existence of Nb prevented recrystallization, here temperature interval makes rolling mill increased load. Because charge press hard against each other,have in the process stay lukewarm course, increased rolling time consequently, reduced manufacturing efficiency. Equivalent of the chemical part that the S355 I-steel that should achieve certain ply wants when the intensity of place correspondence, carbon and Nb content. Need strength to reach place, can use different chemical part. With alloy design principle photograph is compared, c content rose 0. 06 % , nb (V) content is reduced. The intensity of these two kinds of composition is same, be opposite however the impact of tenacity is very big. C content is low, when using Nb microalloy to change, the tenacity of length direction rose, but increase as ply, contented tenacity requirement is more difficult. Solder about ocean more strict tenacity requirement raised in the EN10225 standard of structural steel, this standard is involved transverse or the tenacity requirement of ply direction, to the steel of inferior carbon content, transverse concussion result asks to rise somewhat, to ply direction tenacity character, can be achieved through reducing S content. Craft charging press hard against each other also is used at producing S460 steel, of course, craft charging press hard against each other cannot produce the biggest ply range. To thicker rolled steel, rolling temperature rises, the cooling rate after make friends is reduced, cause a tissue thereby thick change. To achieve strength demand, must add alloy content. Because solder the requirement of function and carbon are equivalent limitation, still cannot produce the S460 rolled steel of 50mm ply above. 1. 4 craft charging press hard against each other: Quicken refrigeration to be the limitation that overcomes control rolling, cooling craft is quickened after research center of metallurgy of ProfilARBED company combination and company of British iron and steel developed roll steel. In quench + from temper craft in, after last second rolling, water of gush of whole I-steel surface is stimulated cold. Before core is quenched, stop gush water, the outside layer of I-steel is undertaken by the quantity of heat that delivers to surface layer from core from temper. Graph the 5 sketch map that are process of this heat treatment. From eventually roller comes out to enter refrigeration wearing directly, right now temperature is 850 ℃ about, after the surface of whole workpiece is cool, begin the 600 ℃ of lukewarm ≥ from temper. Normally, the temperature on the section that quenchs the precondition of + temper craft is whole I-steel wants even, such, in rolling process, want top to the temperature on I-steel position, namely the joint of leg ministry and waist undertakes alternative refrigeration. Graph the 6 sketch map that are this craft. Use this technology to be able to eliminate the temperature difference on I-steel section. The development of blessing mountain factory of company of Japanese steel tube went with online quicken cooling OLAC (the craft of OnlineAcceleratedcooling) likeness. OLAC already began to apply at be since 1980 in plate production. To thick sectional rolled steel, because cross section form is complex, this technology encounters technical difficulty in the applied respect of this kind of material. Because heat is out of shape,use cool without metabolic, because the dimension of the product and steel grade are very dispersive, the product pledges the quantity is controlled hard. And the acceleration that Japanese steel company developed big I-steel is cooling device. The hot-rolling form that uses earnings of different rolling technology to arrive organizes the place before be like to narrate, the brilliant size that traditional rolling earning reachs is 7 class, granuality of the brilliant when controlling rolling is 9 class about, use granuality of the brilliant when cooling quickly to be able to amount to 11 class. So petty organization also has good tenacity below very low temperature, according to EN10113 special standard, the transition temperature of the 41J when ply amounts to 125mm is in - 50 ℃ are the following. Through stimulating cold when refining an organization, nb refines constituent action to fail to develop, in hot-rolling rolled steel, add Nb to fail to raise tenacity. However, in excel in steel, raised weldability thereby through adding Nb to reduce carbolic equivalent, this is attached most importance to especially to thick rolled steel should. Chemical composition produces data from I-steel industry to the influence of mechanical function in, c, Mn, Nb to succumbing intensity and tensile strength rise very remarkable, and cool quickly particularly apparent. The tenacity of structural steel and organization and chemical composition are concerned, following relation is the steel of structure of F + P about containing Al, this relation results from the research of the person such as Mintz works. VT54(℃ ) = 848 - 565d - 167% pearlite of 05 + - 531%Si + 1490%S - 1379%P - 701%Mn - in 497CR ° type, VT54 is the transition temperature when 54J, d is ferrite grain dimension (Mm) , CR is cooling rate (℃ / Min) . This type makes clear, refine grain, the cooling rate after improving Mn content and press hard against each other is favorable to tenacity, pearlite content is adverse to tenacity. The job of the person such as Irvine still shows free nitrogen is very adverse to tenacity. When optimizing chemical composition, need to be able to consider afore-mentioned elements and weldability integratedly, reduce C content, mn content is achieved 15% when, succumb intensity is high, tenacity is good. Reduce C content, add Nb element to have reduce free nitrogen content, refine an organization, increase strength while also increase the good point such as tenacity. Weldability normally, solder operating rules set execution condition clearly, solder with avoiding to appear cold crack. Because solder to tenacity of hot influence area is differred and be caused,cold crack is, easy generation solders when content of the diffusible hydrogen in solder material is high cold crack, wait for parameter decision by the cooling rate after the rigid of temper by dipping in water of steel and solder. Be opposite to depict the chemical part of steel solder the influence of cold crack sensitivity, offerred different formula, the equivalent that be like carbon (CE) or solder crackle sensitivity comprises Pcm. + of Mn/6 of + of CE = C (+ of V)/S of + of Cr + Mo (+ of Si/30 of + of C of = of Cu + Ni)/15Pcm (5B) of + of V/10 of + of Mo/15 of + of + Ni/60 of Cr)/20 of + of Mn + Cu is cold crack of the generation after avoiding solder, can reach armor plate warm-up constant temperature, this temperature is decided by energy of wiring of content of the diffusible hydrogen in material of ply of carbolic equivalent, rolled steel, solder, solder. Warm-up temperature can have consideration according to the method in the standard such as AWSD11, EN1011 or SEW088, although this method can decide warm-up temperature, but when deciding energy of wiring of the smallest solder, namely the minimum of frit apply metal that Chan Daotian fills, have nothing to do with warm-up temperature. With microalloy of low carbon Nb steel replaces C - the first advantage of Mn steel is do not need warm-up and avoided hard fragile area, expanded to solder the suitable scope of craft. I-steel uses flyer energy to solder () of arc welding of welding wire of 8KJ/cm medicine core, before solder not warm-up. Determine contact is different positional hardness profile, all hardness value all is under 300HV10. Be opposite to solder certainly the influence of rolled steel function, use flat position welding, before solder all not warm-up. Used following technology: Control rolling, quicken refrigeration; I-steel ply is 25mm; Welder art, hand arc solder; Receive head dummy form: Flat position welding, oxyacetylene metal-cutting K groove; Soldering axes direction and rolling direction are perpendicular; Before solder not warm-up; Solder wiring can 10 ~ 12kJ/cm, multi-pass welding. Low carbon microalloy the tenacity of steel hot-rolling product is good. After soldering, the intensity of contact won't be reduced, tenacity is exasperate, the mother capable person of Nb microalloy steel and the tenacity that approach weld junction point still very good. Must point out, have research work story, solder to spread cables energy especially, nb and V are adverse to tenacity, because produced brittleness organization or photograph of carbolic nitride separate out, but this kind of situation is not quite general, normally solder craft is solder of arc of much talk hand, gas to protect solder and arc welding of medical core welding wire, adoption solder wiring energy is inferior, it is 12 ~ 20kJ/cm about. Steel of marine to containing Nb microalloy S460 structure undertook relatively spread cables energy solders experiment. The composition of steel is: 008%C, 001%P, 0002%S, 02%Si, 0044%Al, 0043%Nb. Used craft of QST of control rolling + to produce thick sectional I-steel, its dimension is 360 × 410 × 463mm. Use control rolling, quicken refrigeration; I-steel ply is 57mm; Welder art: Bury arc solder; Receive head dummy form: Flat position welding, v of oxyacetylene metal-cutting semmetry groove; Solder axes direction and make friends Xiang Ping go; Not warm-up; Multi-pass welding, 35kJ/cm of solder wiring energy and 50kJ/cm. Can solder according to marine project the requirement of EN10225 of structural steel standard undertakes soldering experimenting, determine mechanical function. Determined the concussion of the different position such as 2mm of + of metal of apply of the weld junction of ministry of the head, center, root ministry, dissolve, FL transforms curve, test result makes clear, to 47J transition temperature asks to be - 40 ℃ (- 40  ) , and test result was achieved - 60 ℃ (- 80  ) , when using energy of spread cables of 50KJ/cm of classics of craft of the solder that bury arc to solder, brittleness also did not appear on weld junction. Still had cracking endurance test of complete ply CTOD. This experiment method results from England, solder through determining contact crackle is most advanced stretch displacement to decide crackle is broken firm patulous critical value. The result makes clear, HAZ keeps taller rupture tenacity, the least value that the CTOD value of each place is more than EN10225 standard to ask - 10 ℃ 025mm, still had another tests, if bend or CTS, the result makes clear, after energy of classics spread cables solders, each place all has exceedingly good tenacity. The main standard that the application of steel of high strenth structure cites 1 times according to the watch asks, the high strenth steel that produces at present succumbs intensity limits is 345 ~ 460MPa. Choose excel in steel to be able to increase load, or the weight that reduces steel structure below constant load condition, the section of alleviative weight and steel structure and to load means are concerned. Application of excel in steel is succumbed the limitation of intensity, but not be exclusive, additionally a few crucial factors are deflection is mixed miss firm appearance, the music that be like gourd ladle. The Yang model quantity of these phenomena and steel and geometrical appearance are concerned, and with succumb intensity and tensile strength have nothing to do. Use 3 different steel to plant, 3 different geometry section, identical load undertook comparative, steel is planted for S460(ReH ≥ 460MPa) , s355(ReH ≥ 355MPa) , s235(ReH ≥ 235MPa) , the advantage that chooses high strenth steel is clearly. It is with S355 steel fiducial, use S460 steel to be able to reduce weight 14% , and choose S235 to add weight 32% . managing cost of material, use S460 to be saved than S355 about 10% , more economic than S235 about 25% . Building an industry to use another good point of excel in steel was to save production cost. Reduced solder ability especially use up. Use excel in steel to replace S235 steel, reduced truss weight and saved solder material wastage. It is in order to use S355 steel fiducial, use S460 to be able to reduce weight 25% , use S235 to will add weight 70% . The contrast of respect of cost of material is identical also, use S460 to replace S355, reduce cost about 20% , creating cost field, want the job of 2 workers insecurity formerly, after section is reduced, solder material wastage decreased 50% , reduced production cost greatly. Still have additionally a few as economic as what reduce weight to concern, if assemble, lade or carry, because of truss dimension volume is small, minor and reduced a space. The price of material depends on its are mechanical function, be like: Rigid, deflection and succumb intensity, there should be an optimal steel to plant when material application option plan. First-rate succumbs intensity limits is 355 ~ 460MPa. Conclusion uses modern production technology, combinative microalloy is changed, although be opposite very thick sectional structural steel, also can achieve intensity the requirement that taller, tenacity solders weller, more easily. Nb won wide application in structural steel, nb has following advantages: Do not reduce the performance connecting casting of steel, can refine an organization, reduce the content of free nitrogen, raise intensity and weldability effectively can. Steel of contemporary excel in received wide application in the domain such as building, shipping and marine structure, because its were reduced,cost of material is mixed production charge, reduced thereby assemble cost. CNC Milling