The tested Φ244. 48 mm x 15. 11 mm seamless tube is pierced and hot-rolled by Φ340 continuous rolling mill train from Φ360 mm casting bloom of steel 27CrMnMoV (/% : 0.27C

0.25Si

0.92Mn

1.06Cr

0.75Mo

0.009P

0. 003S

0.088V). The effect of 830 ~950 °C water quenching

880 °C. water quenching +600 ~ 680 °C 30 ~ 120 min tempering and 880 °C. double water quenching + 620 ~ 660 °C tempering on structure and properties of the steel tube has been tested and researched. The normal requirement on V150 tube yield and tensile strength is respectively 1 034 〜1 241 MPa and N1 103 MPa

and horizontal impact energy at 0°C≥80 J. Tested results shown that with once quenched + tempered at 630 〜655 °C for 60 min

the Mo and V carbides in steel precipitate to produce secondary hardening

the yield and tensile strength of steel are respectively 1 034 - 1 150 MPa and 1 103 ~ 1 225 MPa

and horizontal impact energy of steel at 0°C is 80 ~ 108 J

while with double quenched + tempered at 635 ~655 °C for 60 min the steel gets fine austenite grains by circle quenching

the strength and toughness of steel increase and improve markedly

its yield and tensile strength are respectively 1 034 ~ 1 170 MPa and 1 103 ~ 1 240 MPa

and horizontal impact energy at 0°C is 80 - 120 J. As compared with once quenching + tempering process the stability control of properties of V150 high anti-collapse casing more easily realizes by double quenching + tempering process.