Process for making a welded steel tubular having a weld zone free of untempered martensite
A process for making an untempered martensite-free welded steel tubular is disclosed. The process includes rapid quenching of the steel tubular without formation of untempered martensite, at rates up to about 1600° F./second. There is no post-weld seam annealing process required. Also a welded steel tubular made in accordance with the disclosed process is described.
1 . A process for making a welded steel tubular, comprising:
a. forming sheet steel having a first edge and a second edge opposite the first edge into a cylindrical shape with the first edge and the second edge disposed substantially parallel to and spaced apart from each other;
b. heating the first edge and the second edge to a pre-selected temperature above an austenizing temperature at which the first edge and the second edge are molten or nearly molten;
c. causing the first edge and the second edge to join together into a welded seam, forming a steel tubular; and
d. rapidly cooling the welded seam to 400° F. or lower;
wherein the cooled welded seam is substantially free of untempered martensite.
2 . The process of claim 1 , further comprising cooling the welded seam at a rate of about 0.58° F./second or greater from the austenizing temperature.
3 . The process of claim 2 , further comprising cooling the welded seam at a rate of about 15° F./second or greater from the austenizing temperature.
4 . The process of claim 3 , further comprising cooling the welded seam at a rate of about 800° F./second or greater from the austenizing temperature.
5 . The process of claim 4 , further comprising cooling the welded seam at a rate of less than about 1600° F./second from the austenizing temperature.
6 . The process of claim 1 conducted in the absence of annealing the welded seam after the welded seam is cooled.
7 . The process of claim 1 , wherein the steel tubular is not reheated to a temperature above about 1000° F. subsequent to cooling the welded seam.
8 . The process of claim 1 , wherein the steel tubular does not undergo a seam annealing process.
9 . The process of claim 1 , wherein heating the first edge and the second edge causes heating of a first heat affected zone adjacent to the first edge and a second heat affected zone adjacent the second edge.
10 . The process of claim 9 , further comprising cooling the first and the second heat affected zones, wherein the first and the second heat affected zones are substantially free of untempered martensite.
11 . The process of claim 1 , wherein heating the first edge and the second edge comprises use of electric resistance welding.
12 . The process of claim 1 , wherein the pre-selected temperature is at least about 2700° F.
13 . The process of claim 1 , wherein the steel tubular comprises:
a. between about 0.01 wt. % and about 0.1 wt. % carbon, and
b. between about 0.01 wt. % and about 0.2 wt. % niobium.
14 . The process of claim 13 , wherein the steel tubular comprises a weight ratio of niobium to carbon of between about 0.8 and about 2.
15 . The process of claim 1 , wherein the steel tubular comprises:
a. between about 0.001 wt. % and about 0.015 wt. % boron; and
b. between about 0.001 wt. % and about 0.015 wt. % nitrogen;
wherein the weight ratio of boron to nitrogen is between about 0.8 and about 2.1.
16 . A process for making a welded steel tubular, comprising:
a. forming sheet steel having a first edge and a second edge opposite the first edge into a cylindrical shape with the first edge and the second edge disposed substantially parallel to and spaced apart from each other;
b. heating the first edge and the second edge to at least about 2700° F. by electric resistance welding;
c. causing the first edge and the second edge to join together into a welded seam, forming a steel tubular; and
d. rapidly cooling the welded seam to 400° F. or lower at a rate of about 0.58° F./second or faster;
wherein the steel tubular is not heated to a temperature above about 1000° F. subsequent to cooling the welded seam, and
wherein the steel tubular comprises between about 0.01 wt. % and about 0.1 wt. % carbon and between about 0.01 wt. % and about 0.2 wt. % niobium such that the weight ratio of niobium to carbon is between about 0.8 and about 2.1.
17 . A steel tubular product comprising welded steel, the welded steel comprising:
a. between about 0.01 wt. % and about 0.2 wt. % carbon; and
b. between about 0.01 wt. % and about 0.2 wt. % niobium;
wherein the product is substantially free of untempered martensite.
18 . The product of claim 17 , wherein the weight ratio of niobium to carbon is at least about 0.8 for carbon concentrations below 0.20 wt. %.
19 . The product of claim 17 , wherein the weight ratio of niobium to carbon is between about 0.8 and about 2.1.
20 . The product of claim 17 , further comprising between about 0.001 wt. % and about 0.015 wt. % boron.
21 . The product of claim 20 , wherein the weight ratio of the niobium and boron to carbon is between about 0.8 and 2.1.
22 . The product of claim 17 , wherein the welded steel was rapidly quenched and made in the absence of seam annealing.
23 . A steel tubular product comprising welded steel, the welded steel comprising between about 0.001 wt. % and about 0.015 wt. % boron and an amount of nitrogen such that the weight ratio of boron to nitrogen is between about 0.8 and about 2.1.
24 . A steel tubular product of claim 23 , wherein the steel is untempered martensite free.
25 . A welded steel tubular made in accordance with the method of claim 1.