20or無縫鋼(gang)管是中碳(tan)結構鋼(gang)，冷熱加工機(ji)(ji)能都不(bu)錯，機(ji)(ji)械機(ji)(ji)能較好，且價(jia)格低、來源廣，所以(yi)應(ying)用廣泛(fan)，它的(de)大(da)弱點是淬(cui)透性低，截面(mian)尺(chi)寸大(da)和要求比較高的(de)工件不(bu)宜采用。

　　無縫鋼管淬(cui)火(huo)(huo)溫度(du)(du)在A3+(3050)℃，在實際操縱中，一般是取上限的。偏高(gao)的淬(cui)火(huo)(huo)溫度(du)(du)可(ke)以使工(gong)件(jian)(jian)加(jia)(jia)(jia)熱(re)速度(du)(du)加(jia)(jia)(jia)快，表面氧化(hua)減少，且(qie)能進步工(gong)效(xiao)。為(wei)使工(gong)件(jian)(jian)的奧氏體平(ping)均(jun)(jun)化(hua)，就(jiu)需要足(zu)夠(gou)的保(bao)溫時(shi)間。假如(ru)實際裝(zhuang)爐量(liang)大，就(jiu)需適當延(yan)長保(bao)溫時(shi)間。不(bu)然(ran)，可(ke)能會泛(fan)起因加(jia)(jia)(jia)熱(re)不(bu)平(ping)均(jun)(jun)造成(cheng)硬度(du)(du)不(bu)足(zu)的現象。但保(bao)溫時(shi)間過(guo)長，也(ye)會也(ye)泛(fan)起晶粒粗大，氧化(hua)脫碳嚴峻的弊病，影響淬(cui)火(huo)(huo)質量(liang)。我們以為(wei)，如(ru)裝(zhuang)爐量(liang)大于工(gong)藝(yi)文件(jian)(jian)的劃定，加(jia)(jia)(jia)熱(re)保(bao)溫時(shi)間需延(yan)長1/5。

　　由(you)于無縫(feng)鋼管(guan)淬透(tou)(tou)性低，故應(ying)(ying)采用冷(leng)卻速度(du)大(da)(da)(da)的(de)(de)10%鹽水(shui)(shui)(shui)溶液。工(gong)(gong)件(jian)(jian)(jian)入水(shui)(shui)(shui)后，應(ying)(ying)該淬透(tou)(tou)，但(dan)不(bu)是冷(leng)透(tou)(tou)，假如工(gong)(gong)件(jian)(jian)(jian)在鹽水(shui)(shui)(shui)中冷(leng)透(tou)(tou)，就有可能使(shi)工(gong)(gong)件(jian)(jian)(jian)開(kai)裂(lie)，這是由(you)于當(dang)工(gong)(gong)件(jian)(jian)(jian)冷(leng)卻到180℃左右(you)時，奧氏(shi)體迅(xun)速轉變為馬氏(shi)體造(zao)成過(guo)大(da)(da)(da)的(de)(de)組織應(ying)(ying)力所致(zhi)。因此，當(dang)淬火(huo)工(gong)(gong)件(jian)(jian)(jian)快冷(leng)到該溫(wen)度(du)區域，就應(ying)(ying)采取緩冷(leng)的(de)(de)方法。因為出(chu)水(shui)(shui)(shui)溫(wen)度(du)難以把握，須憑經驗操(cao)縱，當(dang)水(shui)(shui)(shui)中的(de)(de)工(gong)(gong)件(jian)(jian)(jian)抖(dou)動休止(zhi)，即可出(chu)水(shui)(shui)(shui)空冷(leng)。另外(wai)，工(gong)(gong)件(jian)(jian)(jian)入水(shui)(shui)(shui)宜動不(bu)宜靜，應(ying)(ying)按照工(gong)(gong)件(jian)(jian)(jian)的(de)(de)幾何外(wai)形(xing)，作(zuo)規則運動。靜止(zhi)的(de)(de)冷(leng)卻介質加上靜止(zhi)的(de)(de)工(gong)(gong)件(jian)(jian)(jian)，導致(zhi)硬度(du)不(bu)平均，應(ying)(ying)力不(bu)平均而使(shi)工(gong)(gong)件(jian)(jian)(jian)變形(xing)大(da)(da)(da)，甚至(zhi)開(kai)裂(lie)。

　　20or無(wu)縫鋼管調質件淬火后的硬度應該(gai)達(da)到(dao)(dao)HRC56~59，截面大(da)的可能(neng)(neng)性低些，但不(bu)能(neng)(neng)低于HRC48，不(bu)然，就說明(ming)工件未得到(dao)(dao)完(wan)全淬火，組(zu)(zu)織(zhi)(zhi)中可能(neng)(neng)泛(fan)起索(suo)氏(shi)體甚至鐵素體組(zu)(zu)織(zhi)(zhi)，這種組(zu)(zu)織(zhi)(zhi)通過回(hui)火，仍舊(jiu)留(liu)存在基體中，達(da)不(bu)到(dao)(dao)調質的目的。