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设计了一种低碳Mn-Mo-Nb-Cu-Zr-B钢,经热处理工艺,采用中等冷速冷却,可得到以板条贝氏体为主,含粒状贝氏体和针状铁素体的混合组织,轧态屈服强度大于850MPa,达到X120管线钢的强度要求.TEM观察表明,0.015%Zr(质量分数)添加到钢中形成大量含Zr的复杂的碳氮化物,它们的形状不规则,尺寸约为80～200nm;从形态看,它们在高温形成,并且由于其熔点高,再加热到1200℃时,这种析出物中的Ti、Nb会有部分溶解,使其尺寸有所减小,利于控制奥氏体晶粒长大;其他近椭球形的(Ti,Nb)(C,N)则在加热时逐渐溶解直至消失.由于这种含Zr析出物在钢的基体中均匀分布,加热到高温时,它们会明显阻碍晶界移动,从而使含Zr钢的奥氏体晶粒长大倾向性明显比不含Zr钢小.可见,添加微量Zr能够起到提高钢材焊接性能的作用.
A kind of low-carbon Mn-Mo-Nb-Cu-Zr-B steel was designed. After heat treatment, the slab bainite and granular acicular ferrite Body, the yield strength of rolled state is greater than 850MPa, which meets the strength requirements of X120 pipeline steel.EM observation shows that 0.015% Zr (mass fraction) is added to the steel to form a large amount of complex carbonitrides containing Zr, and their shape is not The size of which is about 80 to 200 nm. From the aspect of morphology, they are formed at a high temperature, and because of their high melting point, Ti and Nb in the precipitate are partially dissolved and re-heated to 1,200 ° C, (Ti, Nb) (C, N) gradually dissolve until disappear when heated.As a result of the Zr-containing precipitates in the steel matrix uniform Distribution, when heated to high temperature, they will significantly obstruct the grain boundary movement, so that the austenite grain growth of Zr-containing steels is obviously smaller than the Zr-free steels.It can be seen that the addition of trace Zr can improve the weldability of steel Role.