Tata Steel Limited

Saurabh Kundu

Prashant Pathak

Rajib Saha

A N Bhagat

Appa Rao Chintha

Basudev Bhattacharya

Amar Nath Bhagat

Badirujjaman Syed

Hrishikesh Shastri

Subrata Mukherjee

Soumendu Monia

Subhankar Das Bakshi

G Senthil Kumar

Vinay V Mahashabde

Sushil Kumar Giri

The present disclosure relates to designing of steel composition for line pipe steel to be used for sour environment. The developed steel of the present disclosure exhibits enhanced tensile properties in accordance with API 5L PSL-2 specification for X-65 grade steel, along with superior hydrogen induced cracking resistance with crack length ratio (CLR) of less than 10%, crack thickness ratio (CTR) of less than 5%, crack sensitivity ratio (CSR) of less than 2%. The developed steel is designed such that it is readily hot/cold formed and welded to form linepipe tubes to be used for the transportation of natural gas or crude oil, especially of sour grade. The present disclosure also provide a method of manufacturing the said steel having the composition of the present disclosure.

Steel composition in accordance with API 5L PSL-2 specification for X-65 grade having enhanced hydrogen induced cracking (HIC) resistance, and method of manufacturing the steel thereof

Present invention discloses a high strength hot rolled steel product with tensile strength at least 1100 MPa and elongation not less than 21%. The steel further has uniform elongation not less than 10% and yield and tensile ratio 0.6-0.7. The steel further has tensile toughness in the range 19-23.5 GPa %. The developed steel is primarily aimed for automotive structural applications and also for many other such as defence where good combination of strength and ductility required is very high. The developed steel product has following composition C: 0.15-0.23, Mn: 0.8-2.1, Si: 0.3-1.1, Cr: 0.8-1.3, Mo: 0.08-0.25, Nb: 0.018-0.035, Ti&#x2014;0.01-0.1 S&#x2014;0.008 max, P&#x2014;0.025 max, Al&#x2014;0.05 to 0.3, N&#x2014;0.005 max. The liquid metal was continuous cast into slab casting. The cast slab was soaked above 1150&#xb0; C. for few hours and subsequently the cast structure was broken by deformation prior to hot rolling. The slab was then hot rolled into strip with thickness not less than 10 mm with finish rolling temperature in austenite region and subsequently cooled to above Ms (martensite temperature) but below Bs (Below Bainite start temperature) to avoid polygonal ferrite. The steel with above mentioned properties was developed using existing hot rolling.

Hot rolled steel product with ultra-high strength minimum 1100MPA and good elongation 21%

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Jamshedpur, India

Saurabh Kundu